Metal cleaning paste



United States Patent 3,275,560 METAL CLEANING PASTE Rene D. Wasserman, Stamford, Conn., and Joseph F. Quaas, Island Park, N.Y., assignors to Eutectic Welding Alloys Corporation, Flushing, N.Y., a corporation of New York No Drawing. Filed May 23, 1962, Ser. No. 196,886 5 Claims. (Cl. 252-101) This application is a continuation-in-part of prior patent application Serial No. 62,874, filed October 17, 1960, now abandoned.

This invention relates to a paste for cleaning metal surfaces, and it more particularly relates to such a paste for removing foreign materials and discoloration caused by thermal or mechanical working.

Various methods have been used for removing from metal surfaces any foreign materials such as oxides, rust and heat discoloration which result from thermal treatment such as welding or from metal removal by mechanical or thermal methods. Various mechanical methods such as abrading, machining and sandblasting have been used to remove surface oxides and other discoloring substances. However, most existing cleaning methods usually employ chemical reactions of various acidic mixtures such as etching and pickling solutions.

These chemical metal cleaning methods require immersion of the section or part to be cleaned within a liquid medium. However, this is impractical for large and cumbersome sections, and large tanks of acid-resisting material are prohibitively expensive and require excessive amounts of acid solutions to fill them. Furthermore, there is an undue danger of eating away too much metal when a metal section to be cleaned is entirely immersed in acid. Various barrel methods have also recently been proposed for cleaning small metal parts by combined chemical and mechanical processes, but these methods are not suitable for cleaning relatively large weldments.

An object of this invention is to provide a means for cleaning metal sections which utilizes a chemical reaction, but does not require immersion of the metal section Within a reagent solution; and

Another object is to provide such a means which may be conveniently applied to any part of a section, particularly a weldment.

In accordance with this invention, a metal-cleaning paste includes a minor amount of from 120% by weight of the paste of fine particles of inert oxide material dispersed within a major amount of from 8099% by weight of the paste of an acid cleaning solution. The acid cleaning solution includes a mixture of strong active concentrated hydrochloric, nitric and sulfuric acids. A particularly effective combination of proportional ranges of percent by weight of these acids with respect to the acid cleaning solution is set forth in the following:

Strengths conventionally available in commercial concentrated grades of these acids.

The particle size of from l99% by weight of the inert oxide material is one micron and smaller, and it incorporates a mixture of -80% by weight of each of silica and aluminum oxide to provide a body for the acid solution making it thixotropic enough to form a stable adherent paste. An inert oxide compound such as aluminum silicate can also be utilized as part of the inert oxide material in a minor amount of from 1.0 to 25.0% by weight of that material in the form of a suspension of 200 mesh particle size and finer within the paste to give it additional body. This aluminum silicate can be provided, for example, in the form of clay, bentonite or other metallic silicates of 200 mesh and finer particle size which permits them to form a suspension in the paste. However any foreign substance which might harmfully react with the acid portion of the solution and interfere with its cleaning ability must be eliminated from these silicates.

Part of the oxide constituent of the paste may also consist of a nonmetallic oxide such as pumice which is abrasive as well as inert. A paste incorporating this abrasive constituent may be used where mechanical rubbing as well as chemical attack is required for quickly removing oxide coatings. When an abrasive paste is used, suflicient time is allowed after application to appropriately advance the chemical cleaning action, and then rubbing with an agent such as a rag or brush completes the combined chemical and mechanical oxide removal. After the metal is cleaned, the reaction products are removed whether the paste is abrasive or not, by water rinsing which both removes the cleaning products and neutralizes any acid residue which might be left upon the metal being cleaned.

The following is a preferred example of a particularly effective formulation of this invention.

The particle size of by weight of the inert oxide material is one micron and smaller, and it is composed of an equal mixture of silica (SiO and aluminum oxide (A1 0 The remaining 20% by weight of the inert oxideconstituents is bentonite of 200 mesh particle size.

This paste is applied to a metal surface such as a weldment to be cleaned. It reacts in a remarkably rapid manner, and tenacious refractory oxides may be removed from metal such as stainless steel, cobalt, tungsten, nickel and their alloys in as little time as four to five minutes. The necessary cleaning time upon other metals may be somewhat longer. This paste is so adherent that it Works as well upon vertical and overhead areas as it does when applied directly on top of a fiat surface. The consistency of this paste somewhat resembles that of the paste used to stick paper together, and it is easily worked and applied smoothly over metallic surfaces, for example, by brush,

spatula or any other convenient dispensing and spreading means. After the metal, such as a welded joint to which this paste has been applied, is thoroughly cleaned either through the chemical action of the paste or with cooperative abrasion, the paste is easily removed and any acid residue neutralized by rinsing with water.

This paste accordingly remarkably well adapted for cleaning a large weldment such as a stainless steel boxtype unit that has been fabricated by welding. The refractory oxides or heat tint formed adjacent to the weld head are easily removed regardless of orientation by applying the paste of this invention over the areas to be cleaned,

and allowing it to remain until the cleaning reaction has sufliciently advanced. Then the paste is washed away and throughly neutralized. With a metal such as stainless steel this cleaning may be fully accomplished within five minutes of cleaning reaction plus the time necessary for rinsing and neutralizing.

The mixture of particles of silica and aluminum oxide of one micron and smaller particle size provides remarkably effective paste-forming properties for the acid solution. The exact reason for this is not known, but it is suspected that the electrostatic properties of these constituents have some effect upon this result. The aluminum oxide also enhances the abrasive characteristics of the paste which can be utilized by rubbing it in where necessary for optimum cleaning action.

The acid formulations of this invention provide remarkably effective activity upon application to various metals and alloys without prohibitive fuming or pitting. In contrast, mixtures outside of the recited formulations are either not active enough, so active that they pit the metal, or fume excessively with the emission of noxious fumes such as brown nitrous oxide. This paste accordingly has remarkably effective cleaning characteristics without tending to damage the metal to which it is applied.

What is claimed is:

l. A metal cleaning paste consisting essentially of a minor amount of from 1--20% by weight of fine particles of inert oxide material dispersed within a major amount of from 80-90% by weight of an active acid cleaning solution, from 1-99% by weight of said inert oxide material consisting essentially of a mixture of approximately equal amounts by weight of each of silica and aluminum oxide of one micron particle size and smaller, the balance of said inert oxide material being approximately 200 mesh and finer particle size above said one micron particle size to give body to said paste, and said active acid cleaning solution comprising the following constituents in the indicated ranges of percentages by weight of said solution:

Proportional range in Acid constituent: percent by weight HCl, concentrated -65 HNO concentrated 10-20 H concentrated 10-20 2. A metal cleaning paste as set forth in claim 1 wherein said conventrated acids are substantially of the following normalities:

.Acid constituent: Concentration HCl, N 13.7 HNO N 10.2 H SO ,N 36.0-37.0

3. A metal cleaning paste as set forth in claim 1 wherein 125% of said inert oxide material is aluminum silicate as a suspension of approximately 200 mesh particle size within the paste to give it body.

4. A metal cleaning paste as set forth in claim 3 wherein said aluminum silicate is clay.

5. A metal cleaning paste as set forth in claim 4 wherein said aluminum silicate is bentonite.

References Cited by the Examiner UNITED STATES PATENTS LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, Examiner.

M. WEINBLATI, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,275,560 September 27, 1966 Rene D. Wasserman et al.

It is hereby certified that error appears in the above mmbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 65, after "paste" insert is column 3, line 28, for "80-90%" read 80-99% column 4, line 8, for "conventrated" read concentrated same column 4, lines 11 to 13, strike out "N", each occurrence, and insert the same after the figures in the right-hand column of the tabulation.

Signed and sealed this 29th day of August 1967.

(SEAL) Anest: ERNEST W. SWIDER EDWARD J. BRENNER Awesling Offioer Commissioner of Patents 

1. A METAL CLEANING PASTE CONSISTING ESSENTIALLY OF A MINOR AMOUNT OF FROM 1-20% BY WEIGHT OF FINE PARTICLES OF INERT OXIDE MATERIAL DISPERSED WITHIN A MAJOR AMOUNT OF FROM 80-90% BY WEIGHT OF AN ACTIVE ACID CLEANING SOLUTION, FROM 1-99% BY WEIGHT OF SAID INERT OXIDE MATERIAL CONSISTING ESSENTIALLY OF A MIXTURE OPPROXIMATELY OXIDE OF ONE MICRO PARTICLE SIZE AND SMALLER, THE BALANCE OF SAID INERT MATERIAL BEING APPROXIMATELY 200 MESH AND FINER PARTICLES SIZE ABOVE SAID ONE PARTICLES SIZE TO GIVE BODY TO SAID PASTE, AND SAID ACTIVE ACID CLEANING SOLUTION COMPRISING THE FOLLOWING CONSTITUENTS IN THE INDICATED RANGES OF PERCENTAGE BY WEIGHT OF SAID SOLUTION: PROPORTIONAL RANGE IN ACID CONSTITUENT: PERCENT BY WEIGHT HCL, CONCENTRATED 55-65 HNO3, CONCENTRATED 10-20 H2SO4, CONCENTRATED 10-20 H2O 5-20 BY AMOUNTS BY WEIGHT OF EACH OF SILICA AND ALUMINUN 